Pedal-governor for electric motors



(No Model.) 2 Sheets-Sheet 1.

V A. G. MoKEE. PEDAL GOVERNOR FOR ELECTRIC MOTORS.-

2 Sheets-Sheet 2.

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A. G. McKEE. PEDAL GOVERNOR FOR. ELEUTRIG MOTORS. No. 520,072. PatentedMay 22, 1894.

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UNrrao STATES PATENT Quince.

ARTHUR GLENN MCKEE, OF STATE COLLEGE, PENN SYLVANIA.

PEDAL-GOVERNCR FOR ELECTRIC MOTORS.

SEECIFIGATION forming part of Letters Patent No. 520,072, dated May 22,1894.

Application filed July 13,1893. Serial No. 480.409. (No model.)

T (0% whom it may concern.-

Be it known that I, ARTHUR GLENN MCKEE, a citizen of the United Statesof America, residing at State College, in the county of Gentre, in theState of Pennsylvania, have invented certain new and useful Improvementsin Pedal- Governors for Electric Motors, of which the following is aspecification.

This invent-ion relates to means for starting, stopping and reversing anelectric motor and for varying the speed thereof.

The device is especially designed for use in the circuit of an electricmotor used for driving a dental engine, but it may be used in thecircuit of an electric motor used for other purposes. In the use of thedental engine, it becomes necessary in the operations upon the teeth ofthe patient to vary the speed of rotation and power of the dental tooldriven thereby; the lowest speed being about one hundred and fiftyrotations a minute for cleaning the thread-like cavities at the roots ofthe teeth; the highest about eighteen hundred revolutions a minute forpolishing the teeth; and between these extremes various speeds are usedfor different operations and upon teeth in different conditions. It isdesirable that the dentist be able to vary the speed and power of thetool as required, and also to stop, start and reverse it instantlywithout changing his position and Without withdrawing either hand fromhis work.

The object of this invention is to provide means under the control ofthe foot of the operator for instantly stopping, starting, varying thespeed of, and reversing the motor, and consequently the dental or otherinstrument.

Figure 1 of the accompanying drawings represents a side elevation ofthis pedal governor. Fig. 2 represents a plan view thereof, the boxcontaining the resistance coils being partly in horizontal section. Fig.3 represents a longitudinal section of the resistance box constituting apart of this governor. Fig. 4 represents diagrammatically an electricmotor, a dental engine driven thereby, and this pedal governor in themotor circuit. Fig. 5 represents a plan of the bottom of the base plate.Fig. 6 represents a vertical transverse section on line 7-7 of Fig. l ofthe vertical plate carrying the several contact studs for varying thespeed and reversing.

The same reference numbers indicate the same parts in all the figures.

The drawings represent this pedal actuated governor 10 disposed in thesupply current of an electric motor 200 used for driving a dental engine300.

The dental engine 300 herein illustrated is that shown and described inUnited States Patent No. 492,432, granted to Charles E. Rhone February28, 1893, to which reference is made for a detailed description, but themotor and its governor may be used in connection with any other dentalengine or other machine where change of speed is desirable.

The electric motor 100 herein illustrated is shunt-wound and the speedthereof is changed by varying the current through the armature, but itmay be so connected with the circuit as to vary the speed by changingthe current through the field magnets.

The rheostatic pedal governor 10 comprises a base plate 11, a resistancebox 30 preferably mounted on said base plate, and a pedal 80 alsomounted on said base plate. This base plate 11 is provided at one endwith a number of binding posts as 12, 13, 14, 15 and 16, which extendthrough holes in said plate, and on its under side with grooves 17 and18 leading from the binding posts 12 and 15 to points under the pedal 70and with grooves 19, 20 and 21 extending from the binding posts 13, 14and 16 to points under the resistance box 30, a number of holes beingmade opposite the said terminals of the grooves through which the wiresdisposed in said grooves and connected with said binding posts may passthrough the base plate. The resistance box is disposed at any convenientpoint either on or off the base-plate 11. In the latter case, it may beplaced under the pedal, or at one side thereof as shown. This box isprovided with any desired number of resistance coils as 31, 32, 33 and34 disposed on'spools fastened to one side thereof. The coils 31 and 32are connected with each other by a wire 35, the coils 32 and 33 by awire 36 and the coils 33 and 34 by a wire 37. A se ries of binding posts40, 41,42, 43, 44 and 45 are disposed in a row on the arc of a circle onthe inner face of a vertical plate which may constitute one of the sidewalls of the resistance box 30, a considerable space being left betweenthe posts 44 and 45. Two similar binding posts 46 and 47 are disposed atconsiderable distance apart on a corresponding arc concentric with thatjust described; and two binding posts 48 and 49 are disposed atconsiderable distance apart on a third are concentric with those onwhich the other binding posts are arranged. A wire 50 connects thebinding post 40 with the outer terminal of the coil 31, a wire 51connects the binding post 41 with the outer terminal of the coil 32through the medium of the wire 35, a wire 52 connects the binding post42 with the outer terminal of the coil 33 through the wire 36, the wire53 connects the binding post 43 with the outer terminal of the coil 34through the wire 37 and the wire 54 connects the binding post 44 withthe inner terminal of the coil 34, said coil being cut out when thecurrent passes through this connection. A wire 55 connects the bindingpost 45 of the outer arc-shaped row with the binding post 43 of the samerow. \Vires 56 and 57 cross each other, the former connecting thebinding post 46 of the middle row with the binding post 49 of theinnermost row and the latter connecting the binding post 47 of themiddle row with the binding post 48 of the innermost row. Conductivestuds 60, 61, 62, 63, 64 and 66 are disposed in an arc-shaped row on theouter face of said vertical plate opposite respectively the binding post40, 41, 42, 43, 44 and 45, the studs 60, 61, 62, 63 and 64 beinginsulated from each other and connected respectively with said bindingposts. An insulating stud 65 is disposed between the studs 64 and 66 andprovided at its upper edge with a rib 67. A conductive strip 70 isdisposed on said plate concentric with the row of studs just described,its upper end being opposite the binding post 46 and connectedtherewith. A conductive stud 72 is disposed in the same are as the strip70 opposite to and connected with the uppermost binding post 47, and aninsulating stud 71 is disposed between said strip 70 and said conductivestud 72. A similar conductive strip 75 is disposed on the outer face ofsaid plate concentric with the strip '70, its'upper end being oppositeto and connected with the binding post 48, and a conductive stud 77 isdisposed in the same are and separated from said strip by an insulatingstud 76, said contact stud 77 being opposite to and connected with thebinding post 49.

The pedal 80 is provided with trunnions S1 and 82 which are journaled inpedestal brackets 83 and 84, mounted on the plate 11. This pedal ispreferably constructed of metal and provided at the heel and toeportions with corrugated soft rubber mats 85 and S6,which by frictionalcontact with the sole of the boot of the operator,tend tohold his footin position on the pedal. A vertical flange 87 extends from the ball tothe toe of the pedal and is preferably cast integral therewith. A hardrubber insulating plate 88 is attached to said cuit is connected.

vertical flange 87. Three spring contacts 90, 91, and 92 are disposed onthe insulating plate 88. The spring contact 90, which is nearest thetoe, touches the series of contact studs 60 to 66 opposite the bindingposts 40 to 46; the middle spring contact 91 being adapted to move in apath corresponding to the middle contact strip 70 and the conductive andinsulating studs 71 and 72 for contact with said strip or studs; and theinnermost spring contact 92 being adapted to move in a path in which thestrip 75, conductive stud 77 and insulating stud 76 are disposed.

A positive wire and negative wire connect the pedal governor with themain supply circuit or with any source of electricity and serve tosupply the current for driving the motor 200. The positive wire 100 isconnected with the exterior binding post 12 and the negative wire 110with the exterior post 15. ires and 121 constitute the terminals of theshunt field circuitof the motorand are connected respectively with theexterior binding posts 13 and 14. A wire connects the exterior bindingpost 16 with one of the commutator brushes of the motor anda wire 131connects the other commutator brush with the negative supply wire 110. Awire 95 connected with the exterior binding post 12, to which thepositive supply wire 100 is connected, extends along the base plate 11,preferably in a groove therein, to a point opposite or nearly oppositeto the pivot of the pedal 80; thence passes upward through a hole insaid plate; then extends along the pedal on the under side thereof tothe inner and outer spring contacts 90 and 92, being connected with bothof said spring contacts and serving to supply current to the armature201 of the motor and also to the shunt circuit passing through the fieldmagnets thereof. For connection with the shunt field circuit of themotor, a wire 96 extends from the interior binding post 48, which isconnected with the inner strip 75 on which the spring contact 92 bears,downward through a hole in the base-plate 11.; thence along a groove inthe underside thereof to the exterior binding post 13, with which oneterminal of the shunt circuit is connected; and a return wire 97connects the interior binding post 14 to which the other terminal of theshunt circuit is attached, with the interior binding post 46 which isconnected with the intermediate strip 70, on which the spring contact 91plays. A wire 98 connected with the spring contact 91, passes along theunder side of the pedal 80 to a point opposite the pivot thereof; thencethrough a hole in the base plate 11 and along the underside of said baseto the exterior binding post 15 to which the negative wire 110 of thesupply cir- For the armature current a wire 99 extends down from thebindingpost 4O opposite the conductive stud 60 of the outer series ofstuds over which the spring contact 92 plays, through the base-plate 11to the exterior binding post 16.

and along a groove therein, to the binding post 16, from which thecurrent passes to the armature through the wire 130.

If the motor is not in use, the pedal is in such position that itsconductive spring contacts 90, 91, and 92 rest upon the insulating studs66, 72, and 77, whereby the circuit is.

broken. These several insulating studs 66, 72 and 77 may all be formedin one piece if desired. The rib or ribs as 67 at the upper edge of oneor all of them serve as stops to arrest the upward movement of the pedalunless special force is used to move the pedal over said stops intocontact with the reversing studs 66, 71 and 76 above said insulatingstuds.

The contact studs hereinbefore referred to and hereinafter included inthe claims may be any suitable form of contact terminals, and the stopstud may be any suitable insulating point.

In the use of this pedal governor in connection with a motor for drivinga dental engine, the pedal 80 is depressed untilits outermost contactspring bears upon either of the conductive studs 64, 63, 62, 61, or 60and the spring contacts 91 and 92 bear against the conductive strips 70and 75. The current then passes from the positive wire connected withthe supply circuit to the exterior binding post 12; thence along thewire 95 to the toe flange of the pedal, where it divides, one partpassing through the spring contact 90 and the other part through thespring contact 92. That part of the currentwhich passes through thespring contact 92 forms the shunt circuit for exciting the field magnetsof the motor. It passes from the spring contact 92 into the conductivestrip 75, thence to the interior binding post 48, thence through thewire 96 to the exteriorbinding post 13, thence through the wire of theshunt circuit to the field magnets, thence through the wire 121 of theshunt circuit from said magnet to the exterior binding post 14, thencethrough the wire 97 to the interior binding post 46 of the resistancebox, thence to the conductive strip 70, thence to the spring contact 91on the toe flange of the pedal, thence through the wire 98 to theexterior binding post 15, where it connects with the negative wire 110of the supply circuit. That part of the current which passes into thecontact spring 90, goes thence into one of the conductive studs 66, 64,63, 62, 61, or 60 according to the position of the pedal. WVhen thepedal is in the position illustrated in Fig. 4, where its spring 90 isincontact with a conducting stud 62, the

current passes from said spring to said stud,

thence to the interior bindingpost 42,through the wire 52 to the coil32, thence through the coil 31 and wire 50 to the interior binding post40, and thence through the wire 99 From the binding post 16 it passesthrough the wire to the commutator brush 220, thence to the armature 201of the motor, thence through the other commutator brush 221 and thencethrough the wire 131 to the negative wire 110 connected with the sourceof supply. When the contact spring 90 is in contact with the conductivestud 64, the current for the armature passes through all the resistancecoils, and the motor and dental drill run at the minimum speed; when thecontact spring 90 rests on the contact stud 60, the motor and machinedriven thereby run at the maximum speed. The speed may be varied byadjust ing the pedal so as to bring the spring 90 into contact with anyof the conductive studs referred to, and any desired number of studs andresistance coils may be employed.

When it is desired to reverse the motor for stopping it and consequentlythe drill or other tool driven thereby, the pedal 80 is thrown up beyondthe insulating studs 65, 71 and 76 and its spring contacts 90, 91 and 92ride over the rib or ribs thereon into contact with the reversingconductive studs 66, 72 and 77. The current of the field circuit is thusreversed by means of the cross wires 56 and 57 connecting the bindingposts 47 and and 49, opposite said studs, with the binding posts 56 and48 opposite the strips 70 and 75. The armature current then passesthrough the wire 55 connecting the conductive studs 66 with theconductive stud 63. This reversal of the current tends to reverse themotor and instantly stops itpreparatory to a reversal. The operator thendepresses the pedal until the spring contacts 90, 91 and 92 rest on theinsulating studs or blocks and the motor and the tool remain stationary.

For reversing the motor for the purpose of changing the direction ofrotation of the dental or other tool, the pedal is swung upward in thesame manner as for stopping, and the spring contacts 90, 91 and 92 arepermitted to rest on the uppermost conductive studs 66, 72 and 77. Themotor is thus instantly reversed and the tool rotated in the oppositedirection as long as desired.

. The reversing mechanism is very useful to effect a quick stoppage ofthe tool. It is also useful in reversing the direction of rotation of atool; especially for polishing, as by turning the polishing disk inreverse direction, it will be quickly unscrewed and released from itsholder and can be removed and another put in its place instantly,without the neces sity of resorting to the use of a screw driver, whichcauses annoyance to the operator and interruption of the work. By thismeans the operator can stop the motor in one half second by the watchwhen running at the highest speed, and can reverse the direction ofrotation in still less time.

A variety of reverse speeds may be obtained by increasing the number ofreversing studs, but for practical purposes a single reversal isordinarily sufficient, that which gives a speed of about four hundredrevolutions a minute being preferable in dental work. The regulation ofthe speed may be IIO ettected by placing the resistance coils in thefield circuit instead of in the armature circuit, but the arrangementhereinbefore described is regarded as preferable as it avoids dangerousreaction of a strong armature on a weak field, which might sometimesunexpectedly change the direction of rotation. It will be observed thatthe reversal is effected by reversing the current through the fieldmagnets. This has a slight advantage over reversing the current in thearmature, which latter method might be adopted. Owing to the retentivityof the iron in the field ot' the motor, the heavy current induced by thereversal is distributed over a greater period of time and so has a lowerpotential, and burning out of the armature is avoided.

I claim as my invention- 1. In an electric governor, the combination ofa pedal having a spring contact, a vertical series of contact studs forvarying the current, a stop stud, and a'reversing stud disposed adjacentto the stop stud.

2. In an electric governor, the combination of a stop stud, a verticalseries of contact studs for varying the current, disposed on one side ofsaid stop stud, a'reversing stud disposed adjacent to the stop stud onthe other side thereof, and a pedal having a spring contact.

3. In an electric governor, the combination of a contact stud, areversing stud, a stop stud provided with an arresting rib, and apivoted bar carrying a spring contact for engaging said studs.

4:. In an electric governor, the combination of a series of contactstuds, a reversing stud, a stop stud disposed between said contact studsand reversing stud, and provided with an arresting rib, and a pivotedbar carrying a spring contact for engagingsaid stud.

5. In an electric governor, the combination of a pedal having a springcontact, a vertical series of contact studs for varying the current, astop stud, and a reversing stud disposed adjacent to said stop stud, thestuds admitting least direct current to the armature being disposednearest the reversing stud.

6. In an electric governor, the combination of a series of contact studsdiposed in a vertical plane, and a pedal disposed adjacent to saidstuds, said pedal being provided with a contact spring for establishingan electric connection along said studs, said spring having a frictionalcontact with said studs which holds the pedal in adjusted position atany point in its path of motion.

7. In an electric governor, the combination of a vertical plate providedwith two conductive strips and with a series of contact studs, saidstuds and strips being disposed side by side in a vertical plane, and apedal provided with different yielding plates adapted to bear upon saidstrips and studs.

8. In a rheostatic pedal governor for an electric motor, the combinationof a vertical plate provided with arc-shaped conductive strips and anarc-shaped set of conductive studs, resistances connected with saidstuds, a pedal provided with spring contacts engaging said strips andstuds, and circuit wires connected with said strips, studs and pedal.

9. In a rheostatic pedal governor for an electric motor, the combinationof a vertical plate provided with arc-shaped conductive strips and anarc-shaped set of conductive studs, resistances connected with saidstuds, a pedal provided with spring contacts engaging said strips andstuds, circuit wires connected with said strips, studs and pedal andreversing conductive studs in the path of said contacts.

10. In a pedal governor for an electric motor, the combination of avertical set of conductive studs, resistances connected therewith, apedal, provided with contacts wires connected with said studs and pedal,and means operated by said pedal for reversing the current.

11. In a pedal governor for an electric motor the combination of twoconductive strips, reversing studs above said strips, crossing wiresconnecting said reversing studs with said strips, a set of conductivestuds, a set of resistances connected with said studs, a separateconductive stud in arc with said set, a wire connecting said separatestud with one of the set of studs, and a pedal provided with springcontacts for engaging said strips and studs.

12. The combination of electric conductors, a series of contactterminals disposed in a Vertical plane and connected to said conductors,and an oscillating pedal for closing the circuit through any of saidcontact terminals, said pedal having a vertical flange disposed on oneside, said flange carrying a spring contact for electric connection withsaid terminals.

13. The combinationof electric conductors, two vertically disposedconductive strips, connected with said conductors, a vertical series ofcontact studs'also connected with said condoctors, and a pedal having avertical flange disposed on one side, said flange carrying springcontacts adapted to bear upon said strips and studs.

14. The combination of electric conductors, a series of contactterminals disposed in a vertical plane and connected with saidconductors, and an oscillating contact pedal for closing the circuitthrough any of said contact terminals, said pedal having a frictionalcontact which holds it in adjusted position in electric connection witheither contact terminal.

ARTHUR GLENN MOKEE.

